Messenger No.
27 (March 1982)

ADS BibCode:1982Msngr..27....1LAuthor(s)/Affiliation(s):Léna, P.AA(Observatoire de Meudon, Chairman of the STC)Abstract:Since 1978, the structure of ESO involves a Scientific and Technical Committee (STC) which advises the Council on scientific and technical matters. This committee meets twice a year, usually at Garehing; its members are nominated by the Council and their term is 4 years. The STC has 10 members, who are as evenly distributed as possible among member countries, although indeed mainly chosen for their scientific abilities. The chairman is invited to attend Council meetings and to report to the members.

ADS BibCode:1982Msngr..27....1.Author(s)/Affiliation(s):ESOAA(ESO)Abstract:On March 1, 1982, the Federal Council of Switzerland submitted its signed ESO membership document to the French Foreign Ministry (where the ESO documents are kept). With this act Switzerland's ESO membership becomes effective.

ADS BibCode:1982Msngr..27....2RAuthor(s)/Affiliation(s):Rodriguez-Larrain, S.AA(ESO, La Silla)Abstract:Who would believe that there exists another form of life-a social Iife-in this dark nebula of EI Norte Chico? One would immediately assume that in an environment where noise, lights, wine and other types of pollution have been banned deliberately, the swinging species could not evolve in their party-going and mirth. That the sole survivors could only be those vague, unworldly non-drinkers, whose only concern is to generate work and publish it.

ADS BibCode:1982Msngr..27....4LAuthor(s)/Affiliation(s):Lindroos, P.AA(Stockholm Observatory)Abstract:Stars which are so young that they are still contracting and have not yet reached the main sequence are called pre-mainsequence stars or pms stars. Observationally it is possible to distinguish between several categories of pms stars representing different kinds of stars and phases of evolution. An important and very weil observed (though not weil understood) group of such stars are the T-Tauri stars. They are generally found close to the interstellar clouds in which they were born, and compared to normal older stars they exhibit several peculiarities such as: irregular light variations, strong emission lines, high lithium abundance and excess emission both at ultraviolet and infrared wavelengths. If one determines the luminosities and surface temperatures for T-Tauri stars and plots them in an HR-diagram (such as Fig. 1) one finds that they occupy a region weil above the main sequence. This location coincides with theoretical evolutionary tracks for contracting stars with masses of about 1 solar mass, calculated by Iben. Iben's models which are the ones which best agree with the latest observations of pms stars also show that the T-Tauri are younger than a few million years. Because their masses appear to be about that of the sun we identify the T-Tauri stars as the progenitors of solar-type stars.

ADS BibCode:1982Msngr..27....9CAuthor(s)/Affiliation(s):Comte, G.; Lequeux, J.; Stasińska, G.; Vigroux, L.AA(Observatoire de Marseille) AB(Observatoire de Meudon) AC(Observatoire de Meudon) AD(Section d'Astrophysique, GEN Saclay)Abstract:Abundance determination provides a way to study the evolution of galaxies. In conjunction with other properties of galaxies, such as the gas mass fraction, the present rate of star formation or the luminosity, they can help to determine the 3 major quantities which govern the chemical evolution of galaxies: the Initial Mass Function (IMF), the past rate of star formation (SFR), and the amount of heavy elements produced at each generation of stars. Possibilities of abundance determinations in external galaxies are rare. Even in the closest galaxy, the Large Magellanic Cloud, stellar spectra are restricted to supergiants whose complex atmospheres prevent us from obtaining accurate abundances. Spectra or colours of the integrated light of clusters, or galaxies themselves, can give some information. However, this integrated light comes from a mixture of stars of different spectral type, luminosity c1asses and luminosity, its interpretation in terms of abundances is not straightforward (e. g. Tinsley 1980, Fund. Cosm. Phys., 5,287). For external galaxies, H I1 regions provide the most reliable abundances. They are bright enough to be observed in distant galaxies and the emission line intensities are proportional to the abundances of the emitting ions. Two major problems remain in the way to elemental abundances: correction for unseen ions, and the amount of different elements locked in dust grains.

ADS BibCode:1982Msngr..27...11MAuthor(s)/Affiliation(s):Moorwood, A. F. M.AA(ESO)Abstract:The ESO infrared photometer/spectrophotometer, which was first made available at the 3.6-m telescope towards the end of 1980, has considerably expanded the scope for infrared observations on La Silla and has already led to an enlargement of ESO's active infrared community. Improvements made recently in this system plus the fact that a similar one is to be installed on the 1-m telescope later this year makes it timely to review the status and some of the uses being made of this instrument. In addition, this is a convenient opportunity to report on the progress of the F/35 wobbling secondary and the cooled array spectrometer, both of which will increase further the infrared observing possibilities at the 3.6-m in the future. Before discussing these developments specifically, however, I thought I would begin with abrief introduction to the fundamental considerations which affect infrared instrumentation design and to some of the terminology, which I hope will prove useful to readers who are unfamiliar with this subject.

ADS BibCode:1982Msngr..27...14DAuthor(s)/Affiliation(s):de Loore, C.; Mouchet, M.; van Dessel, E. L.; Burger, M.AA(Astrophysical Institute, Vrije Universiteit, Brussels) AB(Astrophysical Institute, Vrije Universiteit, Brussels) AC(Royal Observatory, Uccle, Brussels) AD(Astrophysical Institute, Vrije Universiteit, Brussels)Abstract:Massive X-ray binaries consist of anormal component of spectral type 0 or B which is transferring matter to a compact companion, generally a neutron star, with possibly one exception, Cyg X-1, where the compact component could be a black hole. These compact stars have enormous magnetic fields (of the order of 1012 gauss), and extremely large gravities; accreted matter will be accelerated to velocities of half the light velocity, and guided by the field lines to restricted areas near the magnetic poles, the hot spots. These regions acquire in this way temperatures of the order of 107 K, and X-rays are generated. The X-rays are transported outwards as beams, and since the compact objects rotate rapidly, X-rays are observed as pulse-shaped beams.

ADS BibCode:1982Msngr..27...17KAuthor(s)/Affiliation(s):Kubiak, M.AA(Warsaw University Observatory and Observatorium Hoher List)Abstract:The reason why stars do sometimes pulsate seems to be satisfactorily explained by the present theory of stellar stability. The small but "irritating" exception is only the group of ßCephei stars: the physical mechanism of their variability remains till today essentially unknown. Observational characteristics of these stars can be summarized as foliows: (i) they are located in a rather narrow instability strip on the H-R diagram in the vicinity of elfective temperature of about 20,000° or spectral types B1-B2; (ii) periods are of the order of a few (3-6) hours; (iii) in some cases the shape of spectrallines varies with phase, the lines being broad on the descending and narrow on the ascending branch of the radial velocity curve; (iv) radial velocity curves are sometimes asymmetric or even discontinuous, particularly for the stars with large amplitudes; (v) maximum light occurs near the phase when the descending branch of the radial velocity curve crosses the mean velocity; (vi) in some of these stars two or more close frequencies are excited; in two cases triplets of equally spaced frequencies are observed.

ADS BibCode:1982Msngr..27...19SAuthor(s)/Affiliation(s):Shaver, P. A.; Danks, A. C.; McGee, R. X.; Newton, L. M.; Pottasch, S. R.AA(ESO) AB(ESO) AC(CSIRO Division of Radiophysics, Sydney) AD(CSIRO Division of Radiophysics, Sydney) AE(Kapteyn Astronomical Institute, Groningen)Abstract:The study of chemical abundances and their variation from one galaxy to another or within individual galaxies is of fundamental importance for our understanding of the evolution of galaxies. The abundances of heavy elements in the interstellar medium provide a fossil record of the enrichment which has taken place due to nucleosynthesis in successive generations of stars. Gradients of heavy element abundances with distance from the galaclic centre are predicted by models in which the rate of star formation varies across the galactic disk, and by dynamical collapse models of galaclic evolution which involve fresh infall of primordial gas onto the disk over long periods of time. Different models predict different abundance gradients (in slope and shape). and abundance measurements give constraints on these models (see Pagel and Edmunds, 1981, Ann. Rev. Astron. Astrophys. 19, 77, for arecent review).

ADS BibCode:1982Msngr..27...22GAuthor(s)/Affiliation(s):Gehren, T.AA(Max-Planck-Institut für Astronomie, Heidelberg)Abstract:The formation of our Galaxy and its evolution from an extended spherical halo to a highly flattened spiral disk can be convincingly documented by observing cool dwarf stars that have remained essentially unevolved since they formed billions of years ago. Model predictions of nucleosynthesis in stars, starting from a zerometal primordial composition, combined with a theoretical outline of the galactic collapse, have led to a coarse description of the history of our Galaxy, in which the oldest stars are extremely metal-poor and have highly eccentric galactic orbits with relatively small orbital angular momenta as compared with young disk stars.

ADS BibCode:1982Msngr..27...25VAuthor(s)/Affiliation(s):Veillet, C.AA(CERGA, Grasse)Abstract:In astronomy, as in other matters, the charm 01 novelty is one of the important lactors that govern the choice 01 the observations. How many objects saw suddenly many eyes or kinds of detectors looking at them, before linding again, some months or years later, their sidereal quietness! ... However, it is often after a long time of regular observations that they confide a (smalI) part 01 their secrets. The laint satellites 01 planets don't transgress this fortunately approximative rule. The deliciency in observations during many consecutive years makes the determination 01 their motion very difficult, and it is olten too late to make up lor lost time. We shall try to i1lustrate this lact in the next lines using the observations of the systems of Saturn, Uranus and Neptune we made in April 1981 on the DanishESO 1.5-m reflector.

ADS BibCode:1982Msngr..27...29VAuthor(s)/Affiliation(s):Valentijn, E.AA(ESO)Abstract:The ESO 40-mm electronographic McMullan camera was delivered for general use at the 3.6-m telescope in April 1980 and has been used since then at regular intervals. A description of the camera, which can be mounted on both triplet correctors of the 3.6-m telescope, has been given in the Messenger No. 17.